A standard chuck is known, as for example from German utility model 7,222,008, having a chuck body defining a chuck axis and formed with an annular body surface centered on this axis, lying in a plane substantially perpendicular to the axis, and facing in one axial direction. A plurality of generally angularly equispaced and radially displaceable jaws are slidable in guides on this chuck body. A tightening sleeve is rotatable on the body about its axis and is effective to displace the jaws radially inwardly on rotation of this sleeve on the body in one rotational sense and for permitting radial outward displacement of the jaws on rotation in the opposite sense.
A bearing ring is normally threaded onto such a chuck body and has a bearing-ring surface that axially confronts and is spaced from the annular body surface. A plurality of roller elements is provided between and riding on the body and the ring surfaces to reduce friction between these two elements. It is standard practice to provide a radially extending setscrew on the bearing ring for preventing unscrewing of this bearing ring.
Such an arrangement requires that extremely careful tolerances be maintained during machining of the various surfaces and screw threads. The body and ring surfaces must be perfectly parallel to each other and perpendicular to the rotation axis of the chuck in order to prevent jamming of the roller elements. Furthermore it is not uncommon for the bearing ring to loosen, as during drilling forces effective between the chuck body and tightening sleeve normally have an angular component capable of unscrewing the bearing ring.
When the chuck described above is used for hammer drilling the first part to fail is normally the bearing. This type of failure is particularly common in self-tightening chucks such as described in my copending patent applications Ser. Nos. 011,772, 011,773 and 011,774 all filed Feb. 13, 1979.